Punctuated equilibrium

Punctuated equilibrium is a theory of evolution which postulates that changes such as speciation can occur very quickly, with long periods of little change (equilibria) in between. This theory explains the evolutionary patterns of species as observed in the fossil record, particularly the relatively sudden appearance of new species in a geologically short time period.

Table of contents

1 The theory and history of the concept 2 Misconception of the theory 3 Simulations of punctuated evolution 4 Literature 5 External links

The theory and history of the concept

The theory of punctuated equilibrium was proposed by Niles Eldredge and Stephen Jay Gould in the 1970s. It relies heavily on Ernst Mayr's concept of peripatric speciation, and it is usually contrasted with phyletic gradualism, though critics, notably Richard Dawkins, have argued that phyletic gradualism is merely a straw man. The actual differences between the various evolution theorists are not as large as the opponents of punctuated equilibrium have suggested (Gould himself said that punk eek, as it is affectionately called, did not in fact refute Darwin's gradualism theories, just added to them the ideas of catastrophism and stasis) and the current debate is often more a debate on the relative degree of punctualism and gradualism than one between two fully different extremes.

Misconception of the theory

The theory of punctuated equilibrium is often misstated as being an explanation for purported "gaps in the fossil record", i.e. the so-called "missing links". However, this confuses two levels of evolution. It merely explains the small jumps that are observed in fossil lineages within or between closely related fossil species, not the transitions between major categories of organisms. Due to the rarity of preservation and the likelihood that speciation occurs in small populations during geologically short periods of time, transitions between species are uncommon in the fossil record. However, transitional fossils at higher taxonomic levels are abundant.

Simulations of punctuated evolution

Recently, computer simulations have provided some insight into how punctuated evolution may work: The equilibrium periods show a gradual accumulation of neutral mutations, and the jump occurs when some beneficial combination of them reaches a certain threshold percentage.

See also: Adaptive radiation

Literature

• N.Eldredge, S.J.Gould:"Punctuated equilibria: an alternative to phyletic gradualism'' in: T.Schopf (Hrsg.), Models in Paleobiology, 82-115, Freeman, Cooper and Co., San Francisco, (1972); wieder abgedruckt in: N.Eldredge, Time frames, Princeton Univ.Press, Princeton, N.J., 1985, 2

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